Motor driving control device and motor driving control method

ABSTRACT

A motor driving control device drives each of a first motor and a second motor based on a predetermined condition designation signal, and includes a control unit, a first motor driving unit and a second motor driving unit. The control unit outputs first and second PWM signals to control driving of the first and second motors, respectively. Each of the first and second motor driving units flow a current through the first and second motors based on the first and second PWM signals, respectively. The control unit includes a determination means configured to determine whether the condition designation signal meets a predetermined mode switching condition, and an adjustment means configured to perform overlapping-related adjustment of an on period of the first PWM signal and an on period of the second PWM signal, based on a determination result of the determination means.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2019-021971, filed Feb. 8, 2019, which is hereby incorporated byreference in its entirety.

BACKGROUND Technical Field

The present disclosure relates to a motor driving control device and amotor driving control method, and in particular to a motor drivingcontrol device that drives a plurality of motors and a motor drivingcontrol method to drive a plurality of motors.

Background

Examples of a device using a motor includes a device having a pluralityof motors as driving sources, for example. Some of motor driving controldevices each driving such a device having a plurality of motors controlthe plurality of motors based on a single input signal. Examples of adevice using such a motor driving control device include acounter-rotating blower that has a structure in which two axial flowfans different from each other in rotation direction of an impeller arestacked in a rotation axis direction.

Japanese Patent Application Laid-Open No. H09-331696 discloses a motordriving device that drives each of a plurality of motors and suppressesfluctuation of a power supply voltage by shifting phases of pulses ofPWM signals to be supplied to respective motor driving units in order todownsize smoothing capacitors.

SUMMARY

In a device using a motor, there is a need to suppress the maximum valueof the power supply current flowing through the whole of the devicedepending on a situation. To meet such a need, it is desirable tosuppress the maximum value of the power supply current flowing throughthe plurality of motors under a specific situation. The configurationdisclosed in Japanese Patent Application Laid-Open No. H09-331696described above, however, cannot suppress the maximum value of the powersupply current flowing through the plurality of motors in some cases.

The present disclosure is related to providing a motor driving controldevice and a motor driving control method capable of suppressing themaximum value of the power supply current flowing through the pluralityof motors.

In accordance with one aspect of the present disclosure, a motor drivingcontrol device drives each of a first motor and a second motor based ona predetermined condition designation signal, and includes a controlunit configured to output a first PWM (pulse width modulation) signal tocontrol driving of the first motor and a second PWM signal to controldriving of the second motor, a first motor driving unit configured toflow a current through the first motor based on the first PWM signal,and a second motor driving unit configured to flow a current through thesecond motor based on the second PWM signal. The control unit includes adetermination means configured to determine whether the conditiondesignation signal meets a predetermined mode switching condition, andan adjustment means configured to perform overlapping-related adjustmentof an on period of the first PWM signal and an on period of the secondPWM signal, based on a determination result of the determination means.

Preferably, the control unit operates in a first control mode in a casewhere the determination means does not determine that the conditiondesignation signal meets the mode switching condition, and operates in asecond control mode in a case where the determination means determinesthat the condition designation signal meets the mode switchingcondition. In the second control mode the adjustment means performs theoverlapping-related adjustment so that an overlapping amount of the onperiod of the first PWM signal and the on period of the second PWMsignal is smaller than an overlapping amount in a case where theoperation is performed in the first control mode.

Preferably, the control unit further includes an upper limit settingmeans configured to set an upper limit value of a sum of the currentflowing through the first motor and the current flowing through thesecond motor, and the upper limit setting means sets the upper limitvalue in the case where the operation is performed in the second controlmode to a value lower than the upper limit value in the case where theoperation is performed in the first control mode.

Preferably, when the operation is performed in the second control mode,the adjustment means performs the overlapping-related adjustment so thatthe sum of the current flowing through the first motor and the currentflowing through the second motor is lower than the upper limit value setby the upper limit setting means.

Preferably, when the control mode is switched from the first controlmode to the second control mode, the control unit reduces a duty ratioof the first PWM signal and a duty ratio of the second PWM signal topredetermined values, and then increases the duty ratio of the first PWMsignal and the duty ratio of the second PWM signal to perform theoverlapping-related adjustment.

Preferably, the motor driving control device further includes a speeddetection means configured to detect a rotational speed of the firstmotor and a rotational speed of the second motor, respectively. Whencontrol operation is performed in the first control mode, the controlunit performs feedback control of the rotational speed of the firstmotor and the rotational speed of the second motor based on a detectionresult of the speed detection means. When the control operation isperformed in the second control mode, the control unit does not performthe feedback control.

Preferably, the adjustment means performs the overlapping-relatedadjustment by adjusting rising timing and a duty ratio of each of thefirst PWM signal and the second PWM signal.

Preferably, the adjustment means performs the overlapping-relatedadjustment by synchronizing one of the first PWM signal and the secondPWM signal with the other signal.

Preferably, the mode switching condition is a prescribed level of thecondition designation signal.

Preferably, the condition designation signal is a pulse signal, and theadjustment means performs the overlapping-related adjustment bysynchronizing the first PWM signal and the second PWM signal with thecondition designation signal.

Preferably, the adjustment means adjusts rising timing of each of thefirst PWM signal and the second PWM signal based on a period of thecondition designation signal and a predetermined delay time to a pulseof the condition designation signal.

Preferably, the mode switching condition is a condition relating to atleast one of a period and a duty ratio of the condition designationsignal.

Preferably, the condition designation signal is a speed command signalthat indicates a target rotational speed of the first motor and a targetrotational speed of the second motor.

In accordance with another aspect of the present disclosure, a motordriving control method is provided to drive each of a first motor and asecond motor based on a predetermined condition designation signal withuse of a first motor driving unit configured to flow a current throughthe first motor based on a first PWM signal to control driving of thefirst motor, and a second motor driving unit configured to flow acurrent through the second motor based on a second PWM signal to controldriving of the second motor, and the motor driving control methodincludes determining whether the condition designation signal meets apredetermined mode switching condition, and performingoverlapping-related adjustment of an on period of the first PWM signaland an on period of the second PWM signal, based on a determinationresult of the determining step.

According to these aspects of the present disclosure, it is possible toprovide a motor driving control device and a motor driving controlmethod capable of suppressing the maximum value of the power supplycurrent flowing through the plurality of motors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a fanaccording to an embodiment of the present disclosure.

FIG. 2 is a timing chart to explain an operation example of a controlunit according to the present embodiment.

FIG. 3 is a first flowchart illustrating an example of a processperformed by a control unit of a motor driving control device.

FIG. 4 is a second flowchart illustrating an example of a processperformed by the control unit.

FIG. 5 is a third flowchart illustrating an example of a processperformed by the control unit.

FIG. 6 is a first diagram schematically illustrating a magnitude ofpower supply currents flowing through motors according to the presentembodiment.

FIG. 7 is a second diagram schematically illustrating the magnitude ofthe power supply current flowing through the motors according to thepresent embodiment.

FIG. 8 is a first diagram explaining overlapping of on periods of PWMsignals and the magnitude of the power supply currents.

FIG. 9 is a second diagram that explains overlapping of the on periodsof the PWM signals and the magnitude of the power supply currents.

FIG. 10 is a third diagram that explains overlapping of the on periodsof the PWM signals and the magnitude of the power supply currents.

FIG. 11 is a block diagram illustrating a configuration of a fanaccording to a variant of the present embodiment.

FIG. 12 is a timing chart explaining an operation example of a controlunit according to the present variant.

FIG. 13 is a flowchart illustrating an example of a process performed bythe control unit according to the present variant.

FIG. 14 is a first diagram schematically illustrating a magnitude ofpower supply currents flowing through motors according to the presentvariant.

FIG. 15 is a second diagram schematically illustrating the magnitude ofthe power supply currents flowing through the motors according to thepresent variant.

DETAILED DESCRIPTION

Hereinafter, a blowing device using a motor driving control deviceaccording to an embodiment of the present disclosure will be described.

Embodiment

FIG. 1 is a block diagram illustrating a configuration of a fan 1according to an embodiment of the present disclosure.

As illustrated in FIG. 1, the fan 1 is a blowing device that includestwo blowers 11 and 12 (first blower 11 and second blower 12) eachincluding an impeller 62. The fan 1 is, for example, a counter-rotatingblower including a structure in which the two axial flow blowers 11 and12 different in rotation direction of the impellers 62 are stacked in arotation axis direction. However, the fan 1 is not limited to thecounter-rotating blower. In the present embodiment, the integral fan 1is configured in such a manner that the two blowers 11 and 12 on aninlet side (intake side) and an outlet side (exhaust side) areintegrally attached to a frame (not illustrated). The fan 1 is, forexample, a fan motor that exhausts heat generated inside an electronicdevice such as an electronic computer and an OA device, to the outsideby wind force, thereby cooling the inside of the electronic device.

More specifically, the fan 1 includes a first motor 21 provided in thefirst blower 11, a second motor 22 provided in the second blower 12, anda motor driving control device 110 that drives each of the first motor21 and the second motor 22 based on a speed command signal (example ofpredetermined condition designation signal) Sc.

The first motor 21 rotates the impeller 62 of the first blower 11. Theimpeller 62 is attached to a rotary shaft of a rotor of the first motor21. Further, the second motor 22 rotates the impeller 62 of the secondblower 12. The impeller 62 is attached to a rotary shaft of a rotor ofthe second motor 22.

The motor driving control device 110 includes a first motor drivingcontrol unit 111 that drives the first motor 21 and a second motordriving control unit 112 that drives the second motor 22.

In other words, the first blower 11 includes the first motor 21 and thefirst motor driving control unit 111, and the second blower 12 includesthe second motor 22 and the second motor driving control unit 112.

Hereinafter, the first motor 21 and the second motor 22 are notdistinguished and are denoted by the motors 21 and 22 in some cases.Further, the first motor driving control unit 111 and the second motordriving control unit 112 are not distinguished and are denoted by themotor driving control units 111 and 112 in some cases.

The motor driving control units 111 and 112 respectively drive themotors 21 and 22. In the present embodiment, each of the motors 21 and22 is, for example, a three-phase brushless motor. The motor drivingcontrol units 111 and 112 periodically flow driving currents throughcoils of the motors 21 and 22 to rotate the motors 21 and 22,respectively.

The fan 1 is connected to a control device 800 that is an externaldevice. In the present embodiment, the control device 800 outputs thespeed command signal Sc corresponding to a rotational speed (rotationalfrequency) of each of the motors 21 and 22, to each of the blowers 11and 12. The speed command signal Sc is input to each of the motordriving control units 111 and 112. The motor driving control units 111and 112 can respectively drive the motors 21 and 22 at the rotationalspeed corresponding to the speed command signal Sc. Note that the motordriving control units 111 and 112 output rotational speed signals S (forexample, FG signals) corresponding to the respective motors 21 and 22.The control device 800 can detect driving states of the blowers 11 and12 based on the rotational speed signals S, and can control the speedcommand signal Sc to be output based on the driving states. Note thatthe rotational speed signals S may not be output to the outside of thefan 1.

In the present embodiment, the first motor driving control unit 111 andthe second motor driving control unit 112 perform substantially the sameoperation except for specific operation in a specific control modedescribed below, and the like.

As described below, the motor driving control device 110 includes acontrol unit (example of adjustment means, and example of upper limitsetting means) 3, a first motor driving unit 2A, and a second motordriving unit 2B. The control unit 3 outputs a first PWM (pulse widthmodulation) signal S4A to control driving of the first motor 21 and asecond PWM signal S4B to control driving of the second motor 22. Thefirst motor driving unit 2A flows a current through the first motor 21based on the first PWM signal S4A. The second motor driving unit 2Bflows a current through the second motor 22 based on the second PWMsignal S4B. Note that FIG. 1 illustrates a part of components of themotor driving control device 110, and the motor driving control device110 may include other components in addition to the componentsillustrated in FIG. 1. Hereinafter, in a case where it is unnecessary todistinguish the first PWM signal S4A and the second PWM signal S4B,operation is described while the signals are collectively referred to asPWM signals S4.

The control unit 3 includes a first control unit 3A and a second controlunit 3B. The first control unit 3A controls driving of the first motor21 by outputting the first PWM signal S4A. The second control unit 3Bcontrols driving of the second motor 22 by outputting the second PWMsignal S4B. The control unit 3 generates the first PWM signal S4A andoutputs the first PWM signal S4A as a driving control signal Sd to thefirst motor driving unit 2A. In addition, the control unit 3 generatesthe second PWM signal S4B and outputs the second PWM signal S4B as thedriving control signal Sd to the second motor driving unit 2B.

In the present embodiment, the first motor driving control unit 111 andthe second motor driving control unit 112 include the same hardwareconfiguration. The first motor driving control unit 111 includes thefirst motor driving unit 2A and the first control unit 3A. The secondmotor driving control unit 112 includes the second motor driving unit 2Band the second control unit 3B. In the following description, componentscommon to the first motor driving control unit 111 and the second motordriving control unit 112 are denoted by the same reference numerals, anddescription of the components is common to the first motor drivingcontrol unit 111 and the second motor driving control unit 112 unlessotherwise noted. Further, the components and the operation are describedwhile the first control unit 3A and the second control unit 3B arecollectively referred to as the control unit 3 when it is unnecessary todistinguish the first control unit 3A and the second control unit 3B,and while the first motor driving unit 2A and the second motor drivingunit 2B are collectively referred to as the motor driving units 2 whenit is unnecessary to distinguish the first motor driving unit 2A and thesecond motor driving unit 2B.

In the present embodiment, each of the motor driving control units 111and 112 is an integrated circuit (IC) device that is partially packaged(for example, control unit 3 and motor driving unit 2). Note that all ofthe motor driving control units 111 and 112 may be packaged as oneintegrated circuit device, or a part or all of the motor driving controlunits 111 and 112 is packaged together with other devices to configureone integrated circuit device.

Each motor driving unit 2 includes an inverter circuit and a pre-drivecircuit. The motor driving units 2 output driving signals to the motors21 and 22 based on the driving control signals Sd output from thecontrol unit 3, thereby driving the motors 21 and 22. In other words,the motor driving units 2 flow currents through the motors 21 and 22 todrive the motors 21 and 22 based on the driving control signals Sdoutput from the control unit 3.

The pre-drive circuits generate output signals to drive the respectiveinverter circuits under the control of the control unit 3, and outputthe output signals to the respective inverter circuits. The invertercircuits output driving signals to the respective motors 21 and 22 basedon the output signals output from the pre-drive circuits, thusenergizing the coils included in the motors 21 and 22.

The speed command signal Sc output from the control device 800 is inputto the control unit 3. Further, the control unit 3 outputs rotationalspeed signals S to the control device 800.

The speed command signal Sc indicates a target rotational speed of thefirst motor 21 and a target rotational speed of the second motor 22. Forexample, the speed command signal Sc is a PWM (pulse width modulation)signal (example of pulse signal) having a duty ratio (on-duty)corresponding to the target rotational speeds of the motors 21 and 22.In other words, the speed command signal Sc is speed command informationcorresponding to target values of the rotational speeds of the motors 21and 22. Note that any pulse signals may be used as the speed commandsignal Sc and the speed command signal Sc may be, for example, a clocksignal having a frequency corresponding to the target rotational speeds.

Further, in the present embodiment, three Hall signals (positiondetection signals) Hu, Hv and Hw are input to the control unit 3 fromeach of the motors 21 and 22. For example, the Hall signals Hu, Hv andHw are output signals of three Hall elements 25 u, 25 v and 25 wdisposed in each of the motors 21 and 22. The Hall signals Hu, Hv and Hware signals corresponding to rotation of the rotor of each of the motors21 and 22. The control unit 3 detects a rotation state of each of themotors 21 and 22 with use of the Hall signals Hu, Hv and Hw, andcontrols driving of the motors 21 and 22. In other words, the controlunit 3 detects the rotational position of the rotor of each of themotors 21 and 22 with use of the Hall signals Hu, Hv and Hw, therebycontrolling driving of the motors 21 and 22. Further, the control unit 3can acquire actual rotational speed information regarding actualrotational speed of the rotor of each of the motors 21 and 22 with useof the Hall signals Hu, Hv and Hw, thereby controlling driving of themotors 21 and 22.

For example, the three Hall elements 25 (one Hall element 25 of each ofmotors 21 and 22 is illustrated for simplification in FIG. 1) outputtingthe respective Hall signals Hu, Hv and Hw are disposed around the rotorof each of the motors 21 and 22 at substantially equal intervals. Thethree Hall elements 25 detect magnetic poles of the rotor of thecorresponding motor 21 or 22 and output the Hall signals Hu, Hv and Hw.

Note that, additionally or alternatively to such Hall signals Hu, Hv andHw, other information regarding the rotation states of the motors 21 and22 may be input to the control unit 3. For example, as the FG signalcorresponding to rotation of the rotor of each of the motors 21 and 22,a signal (pattern FG) generated using a coil pattern provided on asubstrate on the rotor side may be input to the control unit 3. Further,the rotation states of the motors 21 and 22 may be detected based ondetection results of rotational position detection circuits that detecta back electromotive voltage induced in each of phases (U phase, V phaseand W phase) of the motors 21 and 22. An encoder, a resolver, or thelike may be provided to detect information on the rotational speeds ofthe motors 21 and 22.

The control unit 3 is configured by, for example, a microcomputer or adigital circuit. The control unit 3 outputs the driving control signalsSd to drive the motors 21 and 22 based on the input signals. Morespecifically, the control unit 3 outputs the driving controls signals Sdto the motor driving units 2 based on the Hall signals Hu, Hv and Hw.

The control unit 3 outputs, to the motor driving units 2, the drivingcontrol signals Sd to drive the motors 21 and 22, thereby controllingrotation of the motors 21 and 22. The motor driving units 2 outputdriving signals to the motors 21 and 22 to drive the motors 21 and 22,based on the driving control signals Sd.

Each of the first control unit 3A and the second control unit 3Bincludes a rotational speed calculation unit (example of speed detectionmeans) 31 that detects rotational speed of the corresponding motor 21 or22, a speed command analysis unit 32, a PWM command unit 33, a PWMsignal generation unit 35, and a mode determination circuit (example ofdetermination means) 38.

The Hall signals Hu, Hv and Hw output from the corresponding three Hallelements 25 are input to each of the rotational speed calculation units31. Each of the rotational speed calculation units 31 outputs positionalsignals indicating positional relationship between the phases and therotor of the corresponding motor 21 or 22, based on the input Hallsignals Hu, Hv and Hw. Further, the rotational speed calculation units31 generate the actual rotational speed information corresponding toperiods of the positional signals based on the Hall signals Hu, Hv andHw, and output the actual rotational speed information. In other words,each of the rotational speed calculation units 31 outputs the actualrotational speed information regarding actual rotational speed of therotor of the corresponding motor 21 or 22. In the figure, actualrotational frequency signals S2, each including the positional signaland the actual rotational speed information, are illustrated. The actualrotational frequency signals S2 are output to the respective PWM commandunits 33.

The speed command signal Sc is input to the speed command analysis units32. Each of the speed command analysis units 32 outputs a targetrotational speed signal S1 indicating the target rotational speed of thecorresponding motor 21 or 22. The target rotational speed signals S1 arePWM signals each indicating the duty ratio which is identical to theduty ratio of the speed command signal Sc. Each of the target rotationalspeed signals S1 is output to the corresponding PWM command unit 33 andthe corresponding mode determination circuit 38.

The actual rotational frequency signals S2 output from the rotationalspeed calculation units 31 and the target rotational speed signals S1output from the speed command analysis units 32 are input to the PWMcommand units 33. Further, mode setting signals S5 output from the modedetermination circuits 38 described below are input to the PWM commandunits 33. The PWM command units 33 generate PWM setting instructionsignals S3 indicating duty ratios for output of the driving controlsignals Sd based on the input signals, and outputs the PWM settinginstruction signals S3. The PWM setting instruction signals S3 areoutput to the respective PWM signal generation units 35.

The PWM setting instruction signals S3 are input to the respective PWMsignal generation units 35. Further, mode setting signals S5 output fromthe mode determination circuits 38 described below are input to therespective PWM signal generation units 35. The PWM signal generationunits 35 generate respective PWM signals S4 (first PWM signal S4A andsecond PWM signal S4B) to drive the motor driving units 2 based on thePWM setting instruction signals S3. The PWM signals S4 have a duty ratioidentical to the duty ratio of the PWM setting instruction signals S3.In other words, the PWM signals S4 have a duty ratio corresponding tothe PWM setting instruction signals S3.

The PWM signals S4 output from the respective PWM signal generationunits 35 are output as the driving control signals Sd from the controlunit 3 to the motor driving units 2. As a result, the driving signalsare output from the motor driving units 2 to the motors 21 and 22 sothat the motors 21 and 22 are driven.

The mode determination circuits 38 set the control modes of therespective control units 3A and 3B. The target rotational speed signalsS1 are input to the mode determination circuits 38, and the modedetermination circuits 38 output the mode setting signals S5corresponding to the set control modes, based on the input signals. Forexample, the mode setting signals S5 each indicate one of the controlmodes and the other control mode by the high and the low of the voltage(on potential or off potential). However, the mode setting signals S5are not limited to such signals. Each of the mode setting signals S5 isinput to the corresponding PWM command unit 33 and the corresponding PWMsignal generation unit 35.

The mode determination circuits 38 each determine whether a conditiondesignation signal meets a predetermined mode switching condition, andoutput the corresponding mode setting signal S5 based on thedetermination result. The mode switching condition is a conditionrelating to the duty ratio of the speed command signal Sc. Morespecifically, the mode switching condition indicates that the duty ratioof the speed command signal Sc is a value within a predetermined range.Note that the mode switching condition is not limited to theabove-described condition, and may be a condition relating to at leastone of a period and the duty ratio of the speed command signal Sc.

In this case, it can be said that the control unit 3 includes adetermination means determining whether the speed command signal Scmeets the predetermined mode switching condition, and an adjustmentmeans performing overlapping-related adjustment of an on period of thefirst PWM signal S4A and an on period of the second PWM signal S4B basedon a determination result of the determination means. In other words,the motors 21 and 22 are driven by a method for controlling driving of amotor, and the method includes determining whether the speed commandsignal Sc meets the predetermined mode switching condition, andperforming overlapping-related adjustment of the on period of the firstPWM signal S4A and the on period of the second PWM signal S4B based onthe determination result of the determining step.

The control unit 3 includes, as the control modes for controlling themotors 21 and 22, a first control mode and a second control mode.

The first control mode is a normal driving mode in which the motors 21and 22 are driven at the rotational speeds corresponding to the speedcommand signal Sc. In other words, in the first control mode, speedfeedback control of the rotational speed of the first motor 21 and therotational speed of the second motor 22 is performed based on the actualrotational speeds of the respective motors 21 and 22, namely, thedetection results of the respective rotational speed calculation units31, and the speed command signal Sc.

The second control mode is, as will be described later, a control modein which peak current suppression control to suppress a peak currentvalue of a sum of the power supply currents of the motors 21 and 22relative to the peak current value in the first control mode isperformed. In the second control mode a method for outputting the firstPWM signal S4A and the second PWM signal S4B is adjusted to suppress thesum of the power supply currents of the motors 21 and 22 to apredetermined current threshold or less. In other words, when thecontrol operation is performed in the second control mode, the controlunit 3 does not perform the above-described speed feedback control. Inthe present embodiment, the second control mode can be also referred toas a PWM overlapping control mode because overlapping of the on periodof the first PWM signal S4A and the on period of the second PWM signalS4B is adjusted in the second control mode. In the second control modethe control unit 3 as the adjustment means performs overlapping-relatedadjustment so that an overlapping amount of the on period of the firstPWM signal S4A and the on period of the second PWM signal S4B is reducedas compared with the case where operation is performed in the firstcontrol mode.

In a case where it is not determined that the speed command signal Scmeets the mode switching condition, the control unit 3 operates in thefirst control mode. In a case where it is determined that the speedcommand signal Sc meets the mode switching condition, the control unit 3operates in the second control mode. In other words, in the case whereit is determined that the speed command signal Sc meets the modeswitching condition, the adjustment is performed such that theoverlapping amount of the on period of the first PWM signal S4A and theon period of the second PWM signal S4B becomes smaller than theoverlapping amount in the case where it is not determined that the speedcommand signal Sc meets the mode switching condition. As a result, thepeak current value of the sum of the power supply currents of the motors21 and 22 is suppressed as compared with the peak current value in thefirst control mode.

Further, the control unit 3 sets, as the upper limit setting means, anupper limit value (current limit value) of the sum of the currentflowing through the first motor 21 and the current flowing through thesecond motor 22. The upper limit value in the case where the operationis performed in the second control mode, is set lower than the upperlimit value in the case where the operation is performed in the firstcontrol mode. Further, when the operation is performed in the secondcontrol mode, the adjustment means performs the overlapping-relatedadjustment so that the sum of the current flowing through the firstmotor 21 and the current flowing through the second motor 22 is lowerthan the upper limit value set by the upper limit setting means.

In the present embodiment, the operation when such overlapping-relatedadjustment (hereinafter, referred to as overlapping adjustment) of theon period of the first PWM signal S4A and the on period of the secondPWM signal S4B is performed, is specifically performed, for example, bythe PWM command units 33 and the PWM signal generation units 35, as theadjustment means. Further, the operation is performed by, for example,the mode determination circuits 38 as the determination means.

More specifically, each of the mode determination circuits 38 determineswhether the speed command signal Sc meets the predetermined modeswitching condition. In the present embodiment, for example, the factthat the duty ratio of the speed command signal Sc is 5% is defined asthe predetermined mode switching condition. When each of the modedetermination circuits 38 determines that the duty ratio of the speedcommand signal Sc is 5% based on the corresponding target rotationalspeed signal S1, each of the mode determination circuits 38 outputs themode setting signal S5 corresponding to the second control mode. Incontrast, when each of the mode determination circuits 38 determinesthat the duty ratio of the speed command signal Sc is not 5% based onthe corresponding target rotational speed signal S1 (in a case where itis not determined that the duty ratio of the speed command signal Sc is5%), each of the mode determination circuits 38 outputs the mode settingsignal S5 corresponding to the first control mode.

Note that it is preferable that the mode switching condition be set to acondition including a predetermined range. More specifically, forexample, it is preferable that the condition be set such that the speedcommand signal Sc is determined to meet the predetermined mode switchingcondition when the duty ratio of the speed command signal Sc is within arange of 5%±1%.

The PWM command units 33 and the PWM signal generation units 35 areoperated in any of the first control mode and the second control modeindicated by the mode setting signals S5, based on the mode settingsignals S5.

More specifically, in the first control mode, the PWM command units 33and the PWM signal generation units 35 perform the speed feedbackcontrol of the motors 21 and 22 based on the actual rotational frequencysignals S2 and the target rotational speed signals 51 as describedabove. At this time, the first control unit 3A and the second controlunit 3B perform speed feedback control without synchronizing the firstPWM signal S4A with the second PWM signal S4B.

In contrast, in the second control mode, the PWM command units 33 andthe PWM signal generation units 35 perform the overlapping control andoutput the first PWM signal S4A and the second PWM signal S4B. At thistime, the PWM command unit 33 and the PWM signal generation unit 35 ofthe first control unit 3A perform the overlapping adjustment bysynchronizing the first PWM signal S4A with the speed command signal Sc.Further, the PWM command unit 33 and the PWM signal generation unit 35of the second control unit 3B perform the overlapping adjustment bysynchronizing the second PWM signal S4B with the speed command signalSc. In other words, the control unit 3 performs the overlappingadjustment by synchronizing the first PWM signal S4A and the second PWMsignal S4B with the speed command signal Sc.

Further, in the second control mode, the PWM command units 33 and thePWM signal generation units 35 perform the overlapping adjustment byadjusting rising timing (on timing) and the duty ratio of each of thefirst PWM signal S4A and the second PWM signal S4B. Such overlappingadjustment is performed based on the period of the speed command signalSc and a predetermined delay time with respect to a pulse of the speedcommand signal Sc as described below.

FIG. 2 is a timing chart to explain an operation example of the controlunit 3 according to the present embodiment.

In FIG. 2 a waveform of the speed command signal Sc, the control mode ofthe control unit 3, a waveform of the first PWM signal S4A, and awaveform of the second PWM signal S4B are schematically illustrated inorder from an upper side.

As illustrated in FIG. 2, a period T1 of the speed command signal Sc is,for example, 62.5 kHz. For example, when the duty ratio of the speedcommand signal Sc is about 50% as with the duty ratio before time t1,the speed command signal Sc does not meet the predetermined modeswitching condition, and the control unit 3 is operated in the firstcontrol mode.

In the first control mode, the first control unit 3A and the secondcontrol unit 3B each output the corresponding PWM signal S4, a period T2of which is 32 kHz, based on the duty ratio of the speed command signalSc. At this time, the first PWM signal S4A and the second PWM signal S4Bare not synchronized with each other. However, this is notlimitative.Note that the duty ratio of the first PWM signal S4A and the duty ratioof the second PWM signal S4B output corresponding to the same speedcommand signal Sc may be equal to or different from each other.

At time t1, the duty ratio of the speed command signal Sc is set to 5%.As a result, it is determined by the mode determination circuits 38 thatthe speed command signal Sc meets the predetermined mode switchingcondition, and the control unit 3 is operated in the second controlmode. Note that the switching from the first control mode to the secondcontrol mode and the switching from the second control mode to the firstcontrol mode may be immediately performed or may be performed after apredetermined time has elapsed (for example, at a time after timecorresponding to one period of speed command signal Sc has elapsed).

In the second control mode, the first control unit 3A and the secondcontrol unit 3B respectively output the first PWM signal S4A and thesecond PWM signal S4B, with the rising timing of the speed commandsignal Sc as a reference. The first control unit 3A and the secondcontrol unit 3B respectively set the period of the first PWM signal S4Aand the period of the second PWM signal S4B to the period T1 of thespeed command signal Sc. In other words, in the second control mode, thefirst PWM signal S4A and the second PWM signal S4B are output insynchronization with the speed command signal Sc.

At this time, the PWM command units 33 determine the duty ratios of therespective PWM signals S4 to predetermined values, irrespective of theduty ratio of the speed command signal Sc. Further, the PWM signalgeneration units 35 adjusts the rising timing of the first PWM signalS4A and the rising timing of the second PWM signal S4B and output thefirst PWM signal S4A and the second PWM signal S4B, based on the periodof the speed command signal Sc and a predetermined delay time T4 withrespect to the pulse of the speed command signal Sc. Further, the PWMsignal generation unit 35 of the second control unit 3B adjusts therising timing of the second PWM signal S4B in consideration of apredetermined adjustment time T6.

For example, a case where time t2 when the control mode is switched tothe second control mode corresponds to the rising timing of the speedcommand signal Sc is assumed. Further, it is assumed that it takes adelay time T3 from the rising timing of the speed command signal Scuntil the PWM signals S4 are able to be output, and the predetermineddelay time T4 and the predetermined adjustment time T6 are set.

At this time, the PWM signal generation unit 35 of the first controlunit 3A performs adjustment with reference to time t3 after the delaytime T3 has elapsed from time t2 such that the rising timing of thefirst PWM signal S4A comes at time t4 after the predetermined delay timeT4 has elapsed from time t3. In other words, a period T5 from time t4 tothe rising timing of the first PWM signal S4A is zero.

On the other hand, the PWM signal generation unit 35 of the secondcontrol unit 3B performs adjustment such that the rising timing of thesecond PWM signal S4B comes at time t5 delayed from time t4 by theperiod T5 calculated from a predetermined calculation expression. Inother words, the period T5 from time t4 to the rising timing of thesecond PWM signal S4B is not zero, and the rising timing of the secondPWM signal S4B is shifted by the period T5 with respect to the risingtiming of the first PWM signal S4A.

The period T5 from time t4 to the rising timing of the second PWM signalS4B is determined by the following calculation expression. In otherwords, the period T5 is calculated from the calculation expression thatincludes the period T1 of the speed command signal Sc, the predetermineddelay time T4, and the predetermined adjustment time T6 as parameters.Note that the period T5 may be previously calculated and stored in thecontrol unit 3, or the control unit 3 may calculate the period T5 asneeded. The predetermined adjustment time T6 is a value for timingadjustment, and can be appropriately set based on a use application ofthe individual fan 1, various kinds of use conditions, and the like. Ina case where a load and operation characteristics of each of the usedmotors 21 and 22 are changed depending on environmental temperature andthe like, these parameters may be varied based on, for example,temperature detected by a built-in sensor (not illustrated) ortemperature information transmitted from the control device.

T5=(T1/2)−(T4/2)+T6

In the present embodiment, in the second control mode, the duty ratio ofeach of the first PWM signal S4A and the second PWM signal S4B, thepredetermined delay time T4, and the predetermined adjustment time T6are set such that the on period of the first PWM signal S4A and the onperiod of the second PWM signal S4B do not overlap with each other. Notethat, in the second control mode, the on period of the first PWM signalS4A and the on period of the second PWM signal S4B may partially overlapwith each other. In the second control mode, it is sufficient to performadjustment such that the overlapping amount of the on period of thefirst PWM signal S4A and the on period of the second PWM signal S4Bbecomes smaller than the overlapping amount in the case where operationis performed in the first control mode.

As described above, after the control mode is switched to the secondcontrol mode, the overlapping adjustment is performed such that thefirst PWM signal S4A and the second PWM signal S4B are synchronized witheach other with the period identical to the period T1 of the speedcommand signal Sc, and the on period of the first PWM signal S4A and theon period of the second PWM signal S4B do not overlap with each other.

At this time, the PWM command units 33 reduce both of the duty ratio ofthe first PWM signal S4A and the duty ratio of the second PWM signal S4Bto predetermined values when the control mode is switched from the firstcontrol mode to the second control mode. Thereafter, the PWM commandunits 33 increase both of the duty ratio of the first PWM signal S4A andthe duty ratio of the second PWM signal S4B and the overlappingadjustment is performed in that state. At this time, for example, theduty ratio of each of the PWM signals S4 may be reduced once to zero andthen gradually increased, or may be reduced once to a predeterminedvalue close to zero and then reset to a predetermined value higher thanthe predetermined value. Performing such control makes it possible tosurely reduce the power supply current flowing through the fan 1 in thesecond control mode.

A case where the duty ratio of the speed command signal Sc is changedto, for example, 50% at time t8 while the operation in the secondcontrol mode is performed as described above, is assumed. In this case,at time t10 when the current period of the speed command signal Sc ends,each of the mode determination circuits 38 determines that the speedcommand signal Sc does not meet the predetermined mode switchingcondition, and the control unit 3 is operated in the first control mode.

When the control mode is returned to the first control mode, the firstcontrol unit 3A and the second control unit 3B each output thecorresponding PWM signal S4, the period T2 of which is 32 kHz, based onthe duty ratio of the speed command signal Sc. In other words, forexample, when the rising timing of the first PWM signal S4A comes attime t9 after time t8 and before time t10, the next rising timing comesat time t11 after the period T1 from time t9 because the control mode attime t9 is the second control mode. Time t11 is after time t10, and therising timing comes every period T2 thereafter. Further, also in thecase of the second PWM signal S4B, when the rising timing comes aftertime t10, the rising timing comes every period T2. Note that the timingwhen the rising timing of each of the PWM signals S4 is adjusted to thetiming in the first control mode is not limited to the above-describedtiming, and, for example, the timing may be a time after a predeterminedperiod has elapsed from a time when it is determined that the speedcommand signal Sc does not meet the predetermined mode switchingcondition.

Note that the control unit 3 sets the upper limit value of the sum ofthe power supply currents flowing through the first motor 21 and thesecond motor 22. When the sum of the power supply currents exceeds theupper limit value due to load increase or the like, the control unit 3stops output of the driving signals to the first motor 21 and the secondmotor 22. In the present embodiment, the upper limit value of the powersupply currents in the first control mode is set to, for example, 4 A[Ampere] in order to protect the circuit of the first motor 21, thesecond motor 22, and the motor driving control device 110.

In contrast, the upper limit value in the case where the operation isperformed in the second control mode is set to a value smaller than theupper limit value in the case where the operation is performed in thefirst control mode. More specifically, the upper limit value is set to,for example, 0.5 A. When the operation is performed in the secondcontrol mode, the PWM command units 33 and the PWM signal generationunits 35 perform the overlapping adjustment such that the sum of thecurrents flowing through the first motor 21 and the second motor 22becomes lower than 0.5 A as the upper limit value. In other words, theduty ratio of each of the PWM signals S4, the predetermined delay timeT4, and the predetermined adjustment time T6 in the second control modeare set such that the sum of the currents flowing through the firstmotor 21 and the second motor 22 becomes lower than 0.5 A as the upperlimit value.

FIG. 3 is a first flowchart illustrating an example of a processperformed by the control unit 3 of the motor driving control device 110.

In FIG. 3, a flow of the process relating to the setting of the controlmode is illustrated. The process illustrated in FIG. 3 is periodicallyand repeatedly performed.

In step S11, each of the mode determination circuits 38 determineswhether the duty ratio of the speed command signal Sc meets thepredetermined mode switching condition. In other words, each of the modedetermination circuits 38 determines whether the duty ratio of the speedcommand signal Sc is within a predetermined range (for example, withinrange of 5%±1%). When the duty ratio of the speed command signal Sc iswithin the predetermined range (YES), the process proceeds to step S13.Otherwise (NO), the process proceeds to step S12.

In step S12, the control unit 3 sets the control mode to the firstcontrol mode. The PWM command units 33 and the PWM signal generationunits 35 are operated in the first control mode based on the modesetting signals S5 output from the respective mode determinationcircuits 38. As a result, the speed feedback control in the normaldriving mode is performed.

On the other hand, in step S13, the control unit 3 sets the control modeto the second control mode. The PWM command units 33 and the PWM signalgeneration units 35 are operated in the second control mode based on themode setting signals S5 output from the respective mode determinationcircuits 38. As a result, the overlapping adjustment is performed.

When the process in step S12 or step S13 ends, the series of processesends.

Note that, in step S11, it may be determined whether the processproceeds to step S12 or step S13 based on a plurality of determinationresults corresponding to a plurality of periods of the speed commandsignal Sc. This makes it possible to prevent unintentional change of thecontrol mode in a case where the speed command signal Sc is influencedby external factors or the like.

FIG. 4 is a second flowchart illustrating an example of a processperformed by the control unit 3.

In FIG. 4, a flow of the process relating to the setting of the dutyratio of each of the PWM signals S4 (first PWM signal S4A and second PWMsignal S4B) is illustrated. The process illustrated in FIG. 4 isperiodically and repeatedly performed.

In step S21, each of the PWM command units 33 determines whether thecontrol mode is the second control mode. When the control mode is notthe second control mode (NO), the process proceeds to step S22. When thecontrol mode is the second control mode (YES), the process proceeds tostep S23.

In step S22, the duty ratio of each of the PWM signals S4 is set by thenormal speed feedback control. More specifically, the PWM command units33 set the duty ratios of the respective PWM signals S4 based on thetarget rotational speed signals S1 and the actual rotational frequencysignals S2 such that the actual rotational speeds become equal to thetarget rotational speeds. When the process in step S22 ends, the seriesof processes ends.

On the other hand, in step S23, the duty ratio adjustment control isperformed. As a result, in the second control mode, the duty ratio ofeach of the PWM signals S4 is set in a predetermined manner.

More specifically, in step S31, each of the PWM command units 33determines whether the setting of the duty ratio of the correspondingPWM signal S4 is performed for the first time after the control mode isswitched to the second control mode. In a case where the setting of theduty ratio of each of the PWM signals S4 is performed for the first timeafter the control mode is switched to the second control mode (YES), theprocess proceeds to step S32. Otherwise (NO), the process proceeds tostep S33.

In step S32, the PWM command units 33 reduce the duty ratios of therespective PWM signals S4 to predetermined values. For example, the PWMcommand units 33 set the duty ratios of the respective PWM signals S4 tozero. As a result, the duty ratios of the respective PWM signals S4output immediately after the control mode is switched to the secondcontrol mode are zero, which makes it possible to keep the sum of thepower supply currents low.

On the other hand, in step S33, the PWM command units 33 limit themaximum values of the duty ratios of the respective PWM signals S4, andgradually increase the duty ratios of the respective PWM signals S4 toaccelerate the motors 21 and 22. The PWM command units 33 set the dutyratios of the PWM signals S4 to values larger than the previously setduty ratios, for example, until the duty ratios of the PWM signals S4reach the maximum values. This makes it possible to accelerate themotors 21 and 22 while suppressing the sum of the power supply currents.Note that it is desirable that the maximum values of the duty ratios ofthe respective PWM signals S4 be set to the maximum values allowing forthe overlapping adjustment so as not to overlap a high period of thefirst PWM signal S4A and a high period of the second PWM signal S4B (orso as to overlap a high period of first PWM signal S4A and a high periodof second PWM signal S4B within range where the sum of power supplycurrents is allowable). However, the maximum values are not limited tothose values.

When the process in step S33 ends, the duty ratio adjustment controlends, and the series of processes ends.

FIG. 5 is a third flowchart illustrating an example of a processperformed by the control unit 3.

In FIG. 5, a flow of the process relating to the management of therising timing of each of the PWM signals S4 is illustrated. The processillustrated in FIG. 5 is periodically and repeatedly performed.

In step S51, each of the PWM signal generation units 35 determineswhether the control mode is the second control mode. When the controlmode is not the second control mode (NO), the series of processes ends.At this time, the PWM signal generation units 35 output the PWM signalsS4 based on the respective PWM setting instruction signals S3 withoutperforming adjustment of the rising timing. In contrast, when thecontrol mode is the second control mode (YES), the process proceeds tostep S52.

In step S52, each of the PWM signal generation units 35 determineswhether rising of the speed command signal Sc has been detected. Whenrising of the speed command signal Sc is not detected (NO), the processwaits for detection of rising of the speed command signal Sc. Whenrising of the speed command signal Sc is detected (YES), the processproceeds to step S53.

In step S53, the PWM signal generation units 35 stop output of the PWMsignals S4.

In step S54, the PWM signal generation units 35 perform a process forsetting overlapping amount. The PWM signal generation units 35 set thetime T5 from a reference time corresponding to a time when rising of thespeed command signal Sc is detected until the output of the PWM signalsS4 is started, for the first PWM signal S4A and the second PWM signalS4B, respectively.

In step S55, the PWM signal generation units 35 perform a process forsetting output. The PWM signal generation units 35 performs setting tooutput the PWM signals S4 at the duty ratios set by the respective PWMcommand units 33 in the above-described manner.

In step S56, the PWM signal generation units 35 output the PWM signalsS4. When the process in step S56 ends, the series of processes ends.

FIG. 6 is a first diagram schematically illustrating the magnitude ofthe power supply currents flowing through the motors 21 and 22 in thepresent embodiment. FIG. 7 is a second diagram schematicallyillustrating the magnitude of the power supply currents flowing throughthe motors 21 and 22 in the present embodiment.

In FIG. 6 and FIG. 7, the duty ratio of the speed command signal Sc, thecontrol mode, and the waveform of the power supply current areschematically illustrated in order from an upper side. A dashed lineillustrated together with the power supply current indicates the upperlimit value (current limit value) of the sum of the power supplycurrents flowing through the first motor 21 and the second motor 22,which are set by the control unit 3.

FIG. 6 illustrates a case where the control mode is switched from thefirst control mode in which the motors 21 and 22 are normally rotated,to the second control mode, and is then returned to the first controlmode again. In the first control mode, the upper limit value is set to 4A, and the currents flow through the motors 21 and 22 based on the dutyratio of the speed command signal Sc unless the power supply currentsexceed the upper limit value. Thereafter, when the control mode isswitched to the second control mode, the upper limit value is set to 0.5A, and the overlapping adjustment is started. Since the on period of thefirst PWM signal S4A and the on period of the second PWM signal S4B donot overlap with each other because of the overlapping adjustment, apeak of the power supply currents is suppressed at a low level. Further,even if the peak of the sum of the power supply currents rises, the peakdoes not exceed the upper limit value. Note that, when the control modeis switched to the second control mode, the duty ratio of each of thePWM signals S4 is set to a predetermined value (for example, zero), andthen the duty ratio is gradually increased. Therefore, the power supplycurrents are reduced immediately after the control mode is switched tothe second control mode. Thereafter, when the control mode is switchedto the first control mode, the upper limit value is set to 4 A, and thecurrents flow through the motors 21 and 22 based on the duty ratio ofthe speed command signal Sc.

FIG. 7 illustrates a case where the control mode is switched from astate where the motors 21 and 22 are stopped (stop mode), to the secondcontrol mode, and is then returned to the state where the motors 21 and22 are stopped again. When the duty ratio of the speed command signal Scis a stop instruction duty (for example, 1%), the motors 21 and 22 arestopped and the control mode is the first control mode. At this time,the upper limit value is set to 4 A. Thereafter, when the duty ratio ofthe speed command signal Sc becomes 5%, the control mode is switched tothe second control mode, the upper limit value is set to 0.5 A, and theoverlapping adjustment is started. When the control mode is switched tothe second control mode, the duty ratio of each of the PWM signals S4 isset to a predetermined value (for example, zero), and then graduallyincreased to rotate the motors 21 and 22. Thereafter, when the dutyratio of the speed command signal Sc becomes 1%, the control mode isswitched to the first control mode, and the upper limit value is set to4 A. As a result, the currents do not flow through the motors 21 and 22,and the motors 21 and 22 are stopped again.

Depending on a device or a system in which the fan 1 is used, it isdesirable to suppress the sum of the power supply currents flowingthrough the whole of the device or the system, based on the drivingstate of the device or the system. For example, in a case where thepower supply normally used is lost in the device or the system, thedriving is shifted to driving using a battery as an auxiliary powersupply. In a special driving state using such a battery, it is desirableto suppress the peak of the power supply current of the motor used inthe device or the system to a prescribed value or less in order toenable the power supply to last as long as possible.

On the other hand, in a motor device in which a plurality of motors areused like the fan 1, when the on periods of the PWM signals driving theswitching elements to supply power to the respective motors overlap witheach other, the peak values of the power supply currents flowing throughthe motor device are overlapped, and may largely exceed the demandedupper limit value of the power supply currents.

FIG. 8 is a first diagram explaining overlapping of the on periods ofthe PWM signals and the magnitude of the power supply currents.

In FIG. 8, the waveform of the speed command signal Sc, the waveform ofthe first PWM signal S4A, the waveform of the second PWM signal S4B, andthe waveform of the sum of the power supply currents flowing through themotors 21 and 22 in a case where, for example, the motors 21 and 22 areeach rotated at 6200 rotations/min are illustrated in order from anupper side. As illustrated in FIG. 8, when the on period of the firstPWM signal S4A and the on period of the second PWM signal S4B overlapwith each other (in part surrounded by alternate long and two shortdashes line in figure), the power supply current flowing through thefirst motor 21 and the power supply current flowing through the secondmotor 22 are accordingly increased at around the same time. Thus, thesum of the power supply currents flowing through the motors 21 and 22 isincreased (in the illustrated example, value of the peak is about 1.2A).

To meet the above-described demands, for example, a driving controlmethod that constantly shifts phases of the pulses of the PWM signals isconsidered. However, it is difficult for a method for dispersing thepulses of the respective PWM signals with substantially equal intervals,to drive the motors at the rotational speeds as high as possible whilesurely suppressing the sum of the power supply currents to thepredetermined current limit value or less in the special driving stateusing the battery or the like.

In contrast, in the present embodiment, in the special driving state,the speed command signal Sc with the duty ratio of 5% (specific exampleof predetermined mode switching condition) is input to the motor drivingcontrol device 110, which makes it possible to drive the two motors 21and 22 in the second control mode. The duty ratio and the rising timingof each of the PWM signals S4 are adjusted and the overlappingadjustment of the on periods is performed so as to suppress the peakvalue of the power supply currents to a desired threshold or less basedon the demanded current limit value. This makes it possible to suppressthe sum of the power supply currents flowing through the motors 21 and22. Further, in the second control mode, the PWM signals S4 are outputat predetermined duty ratios irrespective of the duty ratio of the speedcommand signal Sc. Therefore, it is possible to drive the motors 21 and22 at relatively high rotational speeds while suppressing the sum of thepower supply currents flowing through the motors 21 and 22. For example,in a case where the fan 1 is used to cool an electronic device, even ifthe normal power supply is lost and the special driving state using thebattery as the power supply is applied, it is possible to operate thefan 1 at higher effective current values while suppressing the powersupply currents to within a prescribed limit.

The switching of the control mode from the first control mode to thesecond control mode can be easily performed by changing the duty ratioof the speed command signal Sc. Since the speed command signal Sc isused to synchronize the first PWM signal S4A with the second PWM signalS4B in the second control mode, the control in the second control modecan be more simply performed.

In the first control mode, the overlapping of the on periods of the PWMsignals is not particularly considered. In other words, in the normalstate, the complicated control to shift the phases of the pulses of thePWM signals is not performed. This makes it possible to reduce an amountof information processed by the control unit 3.

FIG. 9 is a second diagram that explains overlapping of the on periodsof the PWM signals and the magnitude of the power supply currents.

Also in FIG. 9, the waveform of the speed command signal Sc, thewaveform of the first PWM signal S4A, the waveform of the second PWMsignal S4B, and the waveform of the sum of the power supply currentsflowing through the motors 21 and 22 in the case where, for example, themotors 21 and 22 are each rotated at 6200 rotations/min are illustratedin order from an upper side. In FIG. 9, the case where the motors 21 and22 are driven in the second control mode is illustrated. In other words,the overlapping adjustment is performed such that the on period of thefirst PWM signal S4A and the on period of the second PWM signal S4B donot overlap with each other. When the on period of the first PWM signalS4A and the on period of the second PWM signal S4B do not overlap witheach other as described above, the power supply current flowing throughthe first motor 21 and the power supply current flowing through thesecond motor 22 are increased at different times. Accordingly, the sumof the power supply currents of the motors 21 and 22 is suppressed at alow level (in the illustrated example, value of the peak is suppressedto about 0.5 A).

In the case of performing the overlapping adjustment, it is preferableto perform the adjustment such that the phase of the power supplycurrent flowing through the first motor 21 and the phase of the powersupply current flowing through the second motor 22 are opposite in phaseto each other.

FIG. 10 is a third diagram that explains overlapping of the on periodsof the PWM signals and the magnitude of the power supply currents.

In FIG. 10, the waveform of the speed command signal Sc, the waveform ofthe first PWM signal S4A, the waveform of the power supply current ofthe first motor 21, the waveform of the second PWM signal S4B, thewaveform of the power supply current of the second motor 22, and thewaveform of the sum of the power supply currents of the motors 21 and 22in a case where, for example, the motors 21 and 22 are each rotated at7500 rotations/min are illustrated in order from an upper side. FIG. 10illustrates the case where the motors 21 and 22 are driven in the secondcontrol mode, and the rising timing and the duty ratio of each of thePWM signals S4 are set such that the waveforms of the power supplycurrents of the two motors 21 and 22 are opposite in phase to eachother. In this case, it is possible to smooth a synthesized waveform ofthe power supply currents of the motors 21 and 22, and to keep themaximum value of the synthesized power supply current low.

Description of Variant

Hereinafter, a variant of the present embodiment is described. In thefollowing description, components substantially similar to thecomponents in the present embodiment are denoted by the same referencenumerals, and description of such components is omitted in some cases.

In the second control mode, synchronization of the first PWM signal withthe second PWM signal may be performed with one of the first PWM signaland the second PWM signal as a reference. In other words, the controlunit 3 may perform the overlapping-related adjustment by synchronizingone of the first PWM signal and the second PWM signal with the othersignal in the second control mode.

FIG. 11 is a block diagram illustrating a configuration of a fan 1001according to one of the variants of the present embodiment.

As illustrated in FIG. 11, in a motor driving control device 1110 of thefan 1001, the first PWM signal S4A is output from the PWM signalgeneration unit 35 of the first control unit 3A to the control device800, and the first PWM signal S4A is input as is from the control device800 to the PWM command unit 33 of the second control unit 3B.

In the present variant, for example, the fact that the speed commandsignal Sc has a prescribed level is defined as the predetermined modeswitching condition. More specifically, the fact that the speed commandsignal Sc is at a low level or a high level (namely, the duty ratio ofthe speed command signal Sc is 0% or 100%) is defined as thepredetermined mode switching condition. Each of the mode determinationcircuits 38 determines whether the speed command signal Sc meets thepredetermined mode switching condition. Note that it is possible todetermine whether the speed command signal Sc is a signal having aprescribed level, for example, by detecting lapse of a firstpredetermined time after start of an off period (falling of speedcommand signal Sc). Further, it is possible to determine whether thespeed command signal Sc is not a signal having a prescribed level, forexample, from the start of the on period (rising of speed command signalSc) with the predetermined duty ratio while the off period is continuedand lapse of a second predetermined time after the start of the onperiod. Note that one of the low level and the high level of the speedcommand signal Sc may be defined as the predetermined mode switchingcondition. Further, the specific method for determining whether thespeed command signal Sc is the signal having the prescribed level is notlimited to the above-described method.

In the present embodiment, in a case where each of the modedetermination circuits 38 determines that the speed command signal Schas the prescribed level (in case where each of the mode determinationcircuits 38 determines that the duty ratio of the speed command signalSc is 0%), based on the corresponding target rotational speed signal S1,the mode determination circuits 38 output the respective mode settingsignals S5 corresponding to the second control mode. In contrast, in acase where each of the mode determination circuits 38 determines thatthe speed command signal Sc does not have the prescribed level (in acase where each of the mode determination circuits 38 does not determinethat the duty ratio of the speed command signal Sc is 0%), based on thecorresponding target rotational speed signal S1, the mode determinationcircuits outputs the respective mode setting signals S5 corresponding tothe first control mode.

The PWM command units 33 and the PWM signal generation units 35 areoperated in any of the first control mode and the second control modeindicated by the mode setting signals S5, based on the mode settingsignals S5.

In the first control mode, the PWM command units 33 and the PWM signalgeneration units 35 perform speed feedback control of the motors 21 and22 based on the actual rotational frequency signals S2 and the targetrotational speed signals S1 as described above. At this time, the firstcontrol unit 3A and the second control unit 3B perform the speedfeedback control without synchronizing the first PWM signal S4A with thesecond PWM signal S4B.

In contrast, in the second control mode, the PWM command units 33 andthe PWM signal generation units 35 perform the overlapping control andoutput the first PWM signal S4A and the second PWM signal S4B. At thistime, in the present variant, the PWM command unit 33 and the PWM signalgeneration unit 35 of the second control unit 3B perform the overlappingadjustment by synchronizing the second PWM signal S4B with the first PWMsignal S4A. In other words, the control unit 3 performs the overlappingadjustment by synchronizing the second PWM signal S4B with the first PWMsignal S4A.

Further, in the second control mode, the PWM command units 33 and thePWM signal generation units 35 perform the overlapping adjustment byadjusting the rising timing (on timing) and the duty ratio of each ofthe first PWM signal S4A and the second PWM signal S4B. Such overlappingadjustment is performed based on the period of the speed command signalSc and a predetermined delay time with respect to a pulse of the speedcommand signal Sc as described below.

FIG. 12 is a timing chart to explain an operation example of the controlunit 3 according to the present variant.

In FIG. 12, as with FIG. 2, the waveform of the speed command signal Sc,the control mode of the control unit 3, the waveform of the first PWMsignal S4A, and the waveform of the second PWM signal S4B areschematically illustrated in order from an upper side.

As illustrated in FIG. 12, the period T1 of the speed command signal Scis, for example, 62.5 kHz. For example, when the duty ratio of the speedcommand signal Sc is about 50% as with the duty ratio before time t31,the speed command signal Sc does not meet the predetermined modeswitching condition, and the control unit 3 is operated in the firstcontrol mode.

In the example illustrated in FIG. 12, the speed command signal Sc is atthe low level after falling of the speed command signal Sc is detectedat time t31 until time t32 after lapse of a predetermined time (firstpredetermined time) from time t31. Thus, each of the mode determinationcircuits 38 determines that the speed command signal Sc meets thepredetermined mode switching condition (speed command signal Sc hasprescribed level), and the control unit 3 is operated in the secondcontrol mode. Note that the first predetermined time is set to, forexample, a time longer than the period T1 of the speed command signalSc.

In the second control mode, the second control unit 3B outputs thesecond PWM signal S4B with the rising timing of the first PWM signal S4Aalong with output of the first PWM signal S4A by the first control unit3A as a reference. In other words, in the second control mode, thesecond PWM signal S4B is output in synchronization with the first PWMsignal S4A. The first control unit 3A and the second control unit 3Brespectively set the period of the first PWM signal S4A and the periodof the second PWM signal S4B to the period T1 of the speed commandsignal Sc. However, the periods are not limited to the period T1. In thesecond control mode, the period of each of the first PWM signal S4A andthe second PWM signal S4B may still be the period T2, or may bedifferent from both the period T1 and the period T2.

As with the above-described embodiment, in the second control mode, thePWM command units 33 determines the duty ratios of the respective PWMsignals S4 to predetermined values, irrespective of the duty ratio ofthe speed command signal Sc.

In the present variant, the PWM signal generation units 35 outputs thefirst PWM signal S4A and the second PWM signal S4B by adjusting therising timing of the first PWM signal S4A and the second PWM signal S4Bbased on the period T1, the predetermined delay time T4 from time t32when the control mode is switched to the second control mode, and thedelay time T3 with respect to the pulse of the first PWM signal S4A.Further, the PWM signal generation unit 35 of the second control unit 3Badjusts the rising timing of the second PWM signal S4B in considerationof the predetermined adjustment time T6. Note that the delay time T3 isa time caused by operation for signal processing and the like, and ispreviously set as a known time in the PWM signal generation units 35.

When the control mode is switched to the second control mode at timet32, the PWM signal generation unit 35 of the first control unit 3Aperforms adjustment such that the rising timing of the first PWM signalS4A comes at time t33 after the predetermined time T4 has elapsed fromtime t3, with time t32 as a reference. In other words, the period T5from time t33 to the rising timing of the first PWM signal S4A is zero.

On the other hand, the PWM signal generation unit 35 of the secondcontrol unit 3B adjusts the rising timing of the second PWM signal S4Bin the following manner based on the rising timing of the first PWMsignal S4A. The PWM signal generation unit 35 of the second control unit3B can detect the rising timing of the first PWM signal S4A at time t34after the delay time T3 has elapsed from time t33 when the first PWMsignal S4A rises. The PWM signal generation unit 35 of the secondcontrol unit 3B performs adjustment such that the rising timing of thesecond PWM signal S4B comes at time t35 delayed from time t34 by theperiod T5 calculated by a predetermined calculation expression, withtime t34 as a reference. The period T5 from time t34 to the risingtiming of the second PWM signal S4B is not zero, and the rising timingof the second PWM signal S4B and the rising timing of the first PWMsignal S4A are shifted by a time obtained by adding the period T5 andthe delay time T3.

The period T5 is determined by the following calculation expression. Inother words, the period T5 is calculated from the calculation expressionthat includes the period T1 of the speed command signal Sc, the delaytime T3, and the predetermined adjustment time T6 as parameters.

T5=(T1/2)−T3+T6

In the present variant, the duty ratio of each of the first PWM signalS4A and the second PWM signal S4B and the predetermined adjustment timeT6 are set such that the on period of the first PWM signal S4A and theon period of the second PWM signal S4B do not overlap with each other.As described above, in the present variant, after the control mode isswitched to the second control mode, the second PWM signal S4B issynchronized with the first PWM signal S4A, and the overlappingadjustment is performed such that the on period of the first PWM signalS4A and the on period of the second PWM signal S4B do not overlap witheach other.

Note that, also in the present variant, when the control mode isswitched to the second control mode, the duty ratio of the first PWMsignal S4A and the duty ratio of the second PWM signal S4B are bothgradually increased from the predetermined values and the overlappingadjustment is performed. However, the operation is not limited to theabove.

A case where the duty ratio of the speed command signal Sc is changedto, for example, 50%, and the speed command signal Sc rises at time t38while the operation in the second control mode is performed as describedabove, is assumed. In this case, each of the mode determination circuits38 determines that the speed command signal Sc does not meet thepredetermined mode switching condition at time t40 after a predeterminedtime (second predetermined time) has elapsed from time t38. As a result,the control unit 3 is operated in the first control mode from time t40.The second predetermined time may be set to, for example, a time that isthe same as or different from the period T1 of the speed command signalSc.

When the control mode is returned to the first control mode, the firstcontrol unit 3A and the second control unit 3B each output thecorresponding PWM signal S4, the period T2 of which is 32 kHz, based onthe duty ratio of the speed command signal Sc. At this time, in the caseof the first PWM signal S4A in which the rising timing comes at time t39after time t38 and before time t40, the next rising timing comes at timet41 after the period T1 has elapsed from time t39. However, the controlmode is returned to the first control mode at time t41, and the risingtiming thereafter is accordingly adjusted so as to come every period T2.The second PWM signal S4B is adjusted in a similar manner. The secondPWM signal S4B is adjusted such that the rising timing comes everyperiod T2 after the rising timing comes at time t40. Note that thetiming when the period of the rising timing of the PWM signals S4 areadjusted to the periods in the first control mode is not limited to theabove-described timing, and the rising timing may be adjusted to a time,for example, after a predetermined period has elapsed after it isdetermined that the speed command signal Sc does not meet thepredetermined mode switching condition.

FIG. 13 is a flowchart illustrating an example of a process performed bythe control unit 3 according to the present variant.

In FIG. 13, a flow of the process relating to the setting of the controlmode in the present variant is illustrated, as with the flowchartillustrated in FIG. 3 according to the above-described embodiment.

In step S111, each of the mode determination circuits 38 determineswhether the duty ratio of the speed command signal Sc meets thepredetermined mode switching condition. In other words, each of the modedetermination circuits 38 determines whether the duty ratio of the speedcommand signal Sc is 0% or 100%. When the duty ratio of the speedcommand signal Sc is 0% or 100% (YES), the process proceeds to stepS113. Otherwise (NO), the process proceeds to step S112.

In step S112, the control unit 3 sets the control mode to the firstcontrol mode. On the other hand, in step S113, the control unit 3 setsthe control mode to the second control mode. When the process in stepS112 or step S113 ends, the series of processes ends.

FIG. 14 is a first diagram schematically illustrating the magnitude ofthe sum of the power supply currents flowing through the motors 21 and22 according to the present variant. FIG. 15 is a second diagramschematically illustrating the magnitude of the power supply currentsflowing through the motors 21 and 22 according to the present variant.

FIG. 14 and FIG. 15 are illustrated in the same format as the format ofFIG. 6 and FIG. 7. FIG. 14 illustrates the case where the control modeis switched from the first control mode in which the motors 21 and 22are normally rotated, to the second control mode, and is then returnedto the first control mode again. In the first control mode, the upperlimit value (current limit value) of the sum of the power supplycurrents is set to 4 A, and the currents flow through the motors 21 and22 based on the duty ratio of the speed command signal Sc unless the sumof the power supply currents exceeds the upper limit value. Thereafter,when the duty ratio of the speed command signal Sc is changed from 50%to 0%, the control mode is switched to the second control mode, theupper limit value is set to 0.5 A, and the power supply currents aresuppressed at a low level. Thereafter, when the duty ratio of the speedcommand signal Sc is changed to 50%, the control mode is switched to thefirst control mode, the upper limit value is set to 4 A, and thecurrents flow through the motors 21 and 22 based on the duty ratio ofthe speed command signal Sc.

FIG. 15 illustrates the case where the control mode is switched from astate (stop mode) where the motors 21 and 22 are stopped, to the secondcontrol mode, and is then returned to the state where the motors 21 and22 are stopped again. When the duty ratio of the speed command signal Scis a stop instruction duty (for example, 1%), the motors 21 and 22 arestopped and the control mode is the first control mode. At this time,the upper limit value (current limit value) of the sum of the powersupply currents is set to 4 A. Thereafter, when the duty ratio of thespeed command signal Sc becomes 0%, the control mode is switched to thesecond control mode, the upper limit value is set to 0.5 A, and theoverlapping adjustment is started. Thereafter, when the duty ratio ofthe speed command signal Sc becomes the stop instruction duty, thecontrol mode is switched to the first control mode again, and the upperlimit value is set to 4 A. As a result, the currents do not flow throughthe motors 21 and 22, and the motors 21 and 22 are stopped.

Also in the present variant, effects similar to the effects in theabove-described embodiment are achievable. In the present variant, theprescribed level of the speed command signal Sc is defined as thepredetermined mode switching condition. Accordingly, when the motors 21and 22 are driven in the first control mode in the normal state, theduty ratio of the speed command signal Sc can be appropriately setwithin a wide range.

Others

The circuit configuration of the blower and the motor driving controldevice configuring the fan is not limited to the circuit configurationillustrated in the above-described embodiment. Various circuitconfigurations configured to meet the object of the present disclosureare applicable. The blower and the motor driving control device may beconfigured by a combination of some of the features in theabove-described embodiment. In the above-described embodiment, somecomponents may not be provided, or some components may be configured inthe other form.

The fan may not be connected to the control device. For example, twomotor driving control units may be operated based on a single speedcommand signal output from an output unit provided in the motor drivingcontrol device.

The overlapping adjustment of the on periods of the two PWM signals maybe performed also in the first control mode. In other words, theadjustment is performed in the second control mode such that theoverlapping amount of the on period of the first PWM signal and the onperiod of the second PWM signal becomes smaller than the overlappingamount when the operation is performed in the first control mode.

The switching of the control mode may be performed using a signaldifferent from the speed command signal as the condition designationsignal. Further, the synchronization of the first PWM signal with thesecond PWM signal in the second control mode may be performed based on asignal different from the signal used as the condition designationsignal, such as the speed command signal. For example, the two PWMsignals may be synchronized based on a periodic pulse signal. Thecontrol mode may be switched using the condition designation signal thatdesignates the control mode based on a magnitude of a voltage.

The control mode may be switched as with the above-described embodiment,and the synchronization of the first PWM signal with the second PWMsignal may be performed with one of the first PWM signal and the secondPWM signal as a reference in the second control mode as with theabove-described variant.

The fan may include a first blower and a second blower that are disposedso as not to be aligned in the center of the rotation axis. Further, atleast one of the first blower and the second blower may not be an axialflow fan. The fan may include three or more blowers. The motor drivingcontrol device and the motor driving control method are not limited tothe motor driving control device and the motor driving control methodused for the fan. The number of motors driven by the motor drivingcontrol device is not limited to two.

The motor driven by the motor driving control device according to thepresent embodiment is not limited to a three-phase brushless motor, andmay be a motor having the other number of phases or a motor of the othertype. As the energization method for each motor, 120-degree energizationmethod can be adopted. However, the other energization method (forexample, 150-degree energization method) may be adopted. The number ofHall elements is not limited to three. The position detection signal ofthe motor may be acquired using a detector different from the Hallelement. For example, a Hall IC may be used. Further, the motor may bedriven by a sensorless system without using a position detector such asa Hall element and a Hall IC.

Each of the above-described flowcharts and the like illustrates anexample for description of the operation, and is not limited to thedescribed flowchart. The steps illustrated in each of the flowcharts arespecific examples, and are not limited to the flow. For example, theorder of the steps may be changed, the other process may be insertedbetween the steps, or the process may be performed in parallel.

A part or all of the process in the above-described embodiment may beperformed by software or by using a hardware circuit. For example, thecontrol unit is not limited to a microcomputer. The configuration insidethe control unit may be at least partially processed by software.

The above-described embodiment is considered to be illustrative in allrespects and not restrictive. The scope of the present disclosure isdefined by the appended claims rather than the above description. Allchanges or modifications made from the spirit and scope of thedisclosure and equivalents thereof should be construed as falling withinthe scope of the disclosure.

What is claimed is:
 1. A motor driving control device that drives eachof a first motor and a second motor based on a predetermined conditiondesignation signal, the motor driving control device comprising: acontrol unit configured to output a first PWM (pulse width modulation)signal to control driving of the first motor and a second PWM signal tocontrol driving of the second motor; a first motor driving unitconfigured to flow a current through the first motor based on the firstPWM signal; and a second motor driving unit configured to flow a currentthrough the second motor based on the second PWM signal, wherein thecontrol unit includes a determination means configured to determinewhether the condition designation signal meets a predetermined modeswitching condition, and an adjustment means configured to performoverlapping-related adjustment of an on period of the first PWM signaland an on period of the second PWM signal, based on a determinationresult of the determination means.
 2. The motor driving control deviceaccording to claim 1, wherein the control unit operates in a firstcontrol mode in a case where the determination means does not determinethat the condition designation signal meets the mode switchingcondition, and operates in a second control mode in a case where thedetermination means determines that the condition designation signalmeets the mode switching condition, and in the second control mode theadjustment means performs the overlapping-related adjustment so that anoverlapping amount of the on period of the first PWM signal and the onperiod of the second PWM signal is smaller than an overlapping amount ina case where the operation is performed in the first control mode. 3.The motor driving control device according to claim 2, wherein thecontrol unit further includes an upper limit setting means configured toset an upper limit value of a sum of the current flowing through thefirst motor and the current flowing through the second motor, and theupper limit setting means sets the upper limit value in the case wherethe operation is performed in the second control mode to a value lowerthan the upper limit value in the case where the operation is performedin the first control mode.
 4. The motor driving control device accordingto claim 3, wherein, when the operation is performed in the secondcontrol mode, the adjustment means performs the overlapping-relatedadjustment so that the sum of the current flowing through the firstmotor and the current flowing through the second motor is lower than theupper limit value set by the upper limit setting means.
 5. The motordriving control device according to claim 4, wherein, when the controlmode is switched from the first control mode to the second control mode,the control unit reduces a duty ratio of the first PWM signal and a dutyratio of the second PWM signal to predetermined values, and thenincreases the duty ratio of the first PWM signal and the duty ratio ofthe second PWM signal to perform the overlapping-related adjustment. 6.The motor driving control device according to claim 2, furthercomprising a speed detection means configured to detect a rotationalspeed of the first motor and a rotational speed of the second motor,respectively, wherein when control operation is performed in the firstcontrol mode, the control unit performs feedback control of therotational speed of the first motor and the rotational speed of thesecond motor based on a detection result of the speed detection means,and when the control operation is performed in the second control mode,the control unit does not perform the feedback control.
 7. The motordriving control device according to claim 1, wherein the adjustmentmeans performs the overlapping-related adjustment by adjusting risingtiming and a duty ratio of each of the first PWM signal and the secondPWM signal.
 8. The motor driving control device according to claim 1,wherein the adjustment means performs the overlapping-related adjustmentby synchronizing one of the first PWM signal and the second PWM signalwith the other signal.
 9. The motor driving control device according toclaim 8, wherein the mode switching condition is a prescribed level ofthe condition designation signal.
 10. The motor driving control deviceaccording to claim 1, wherein the condition designation signal is apulse signal, and the adjustment means performs the overlapping-relatedadjustment by synchronizing the first PWM signal and the second PWMsignal with the condition designation signal.
 11. The motor drivingcontrol device according to claim 10, wherein the adjustment meansadjusts rising timing of each of the first PWM signal and the second PWMsignal based on a period of the condition designation signal and apredetermined delay time to a pulse of the condition designation signal.12. The motor driving control device according to claim 10, wherein themode switching condition is a condition relating to at least one of aperiod and a duty ratio of the condition designation signal.
 13. Themotor driving control device according to claim 1, wherein the conditiondesignation signal is a speed command signal that indicates a targetrotational speed of the first motor and a target rotational speed of thesecond motor.
 14. A motor driving control method to drive each of afirst motor and a second motor based on a predetermined conditiondesignation signal with use of a first motor driving unit configured toflow a current through the first motor based on a first PWM signal tocontrol driving of the first motor, and a second motor driving unitconfigured to flow a current through the second motor based on a secondPWM signal to control driving of the second motor, the motor drivingcontrol method comprising: determining whether the condition designationsignal meets a predetermined mode switching condition; and performingoverlapping-related adjustment of an on period of the first PWM signaland an on period of the second PWM signal, based on a determinationresult of the determining step.